1. Field of the Invention
The present invention relates to an optical fiber connected body in which optical fibers are connected with each other, which is used in optical communications, an optical connector for forming the same, and a mode conditioner and an optical transmitter optical connector using the same.
2. Description of the Related Art
Systems used for connecting computers include 10-megabit Ethernet (registered trademark) and 100-megabit Fast Ethernet (registered trademark), and they are further to be replaced by gigabit Ethernet (registered trademark) of larger transmission capacity. For superfast large capacity transmission, development has been started for 10-gigabit Ethernet (registered trademark).
For high speed and large capacity of data transmission, transmission system must be changed from electrical signal to optical signal. Optical signal is further demanded to be changed from optical signal emitted by light emitting diode (LED) to optical signal emitted by laser diode (LD). Communication cables are also changed from copper wires to multimode optical fiber and further to single mode optical fiber for the benefits of high speed and large capacity of transmission.
On the other hand, cable networks of the multimode optical fibers are already established, and it is attempted to realize high speed and large capacity transmission by using them. When LD light is put in the multimode optical fiber, since the spot size of LD light is smaller than the core diameter of the multimode optical fiber, the core is not sufficiently filled with light, and excitation is not successful. It is hence devised to put the LD light directly into the single mode optical fiber, and bond it to an existing multimode optical fiber.
In an existing multimode optical fiber, however, a dimple-like portion that is low in refractive index may be formed in the central area as shown in FIG. 19B in its manufacturing process. Accordingly, when the single mode optical fiber receiving the LD light is connected to the multimode optical fiber, some of the modes may be dispersed, and various signals may interfere with each other. As a result, an accurate signal cannot be received in the receiver, and the transmission distance is extremely shortened.
It is hence proposed to connect the single mode optical fiber and the multimode optical fiber by deviating the central axis. For example, Japanese Laid-open Patent Application No. 2001-13375 discloses an optical connector for connecting the single mode optical fiber and the multimode optical fiber by deviating the central axis of cores.
Japanese Laid-open Patent Application No. 2000-231027 discloses a mode conditioner using a patching cord connecting the single mode optical fiber and the multimode optical fiber by deviating the central axis of cores, at the transmission side.
Japanese Laid-open Patent Application No. 2000-147334 discloses an optical transmitter with mode conditioner having a single mode optical fiber eccentric in the central axis of core provided in a fiber stab. To this optical transmitter, a plug ferrule having the multimode optical fiber is connected for making optical transmission.
By using these optical fibers, mode conditioner, and optical transmitter with mode conditioner, the light passing through the single mode optical fiber enters the multimode optical fiber by evading a dimple-like portion low in refractive index formed in the central area as shown in FIG. 19B. Hence, suppressing abnormal dispersion of modes, data can be transmitted efficiently.